Laminate flooring usually consists of a core of a 6-12 mm fibre board, a 0.2-0.8 mm thick upper decorative surface layer of laminate and a 0.1-0.6 mm thick lower balancing layer of laminate, plastic, paper or like material. The surface layer provides appearance and durability to the floor panels. The core provides stability, and the balancing layer keeps the panel plane when the relative humidity (RH) varies during the year. The floor panels are laid floating, i.e. without gluing, on an existing sub floor. Laminate flooring and also many other types of flooring are made by the surface layer and the balancing layer being applied to a core material. This application may take place by gluing a previously manufactured decorative layer, for instance when the fibre board is provided with a decorative high pressure laminate which is made in a separate operation where a plurality of impregnated sheets of paper are compressed under high pressure and at a high temperature. The currently most common method when making laminate flooring, however, is direct laminating which is based on a more modern principle where both manufacture of the decorative laminate layer and the bonding to the fibre board take place in one and the same manufacturing step. Impregnated sheets of paper are applied directly to the panel and pressed together under pressure and heat without any gluing.
Traditional hard floor panels in floating flooring of this type are usually joined by means of glued tongue-and-groove joints.
In addition to such traditional floors, which are joined by means of glued tongue-and-groove joints, floor panels have recently been developed which do not require the use of glue and instead are joined mechanically by means of so-called mechanical locking systems. These systems comprise locking means, which lock the panels horizontally and vertically. The mechanical locking systems are usually formed by machining of the core of the panel. Alternatively, parts of the locking system can be formed of a separate material, for instance aluminium or HDF, which is integrated with the floor panel, i.e. joined with the floor panel in connection with the manufacture thereof.
The main advantages of floating floors with mechanical locking systems are that they can easily and quickly be laid by various combinations of inward angling, snapping-in and insertion. They can also easily be taken up again and used once more at a different location. A further advantage of the mechanical locking systems is that the joint edges of the floor panels can be made of materials, which need not to have good gluing properties. The most common core material is fibreboard with high density and good stability usually called HDF—High Density Fibreboard. Sometimes also MDF—Medium Density Fibreboard—is used as core.
Definition of Some Terms
In the following text, the visible surface of the installed floor panel is called “front side”, while the opposite side of the floor panel, facing the sub floor, is called “rear side”. The edge between the front and rear side is called “joint edge”. By “horizontal plane” is meant a plane, which extends parallel to the outer part of the surface layer. Immediately juxtaposed upper parts of two adjacent joint edges of two joined floor panels together define a “vertical plane” perpendicular to the horizontal plane.
By “joint” or “locking system” are meant co acting connecting means, which connect the floor panels vertically and/or horizontally. By “mechanical locking system” is meant that joining can take place without glue. Mechanical locking systems can in many cases also be combined with gluing. By “integrated with” means formed in one piece with the panel or factory connected to the panel.
By a “flexible tongue” is meant a separate tongue which has a length direction along the joint edges and which is forming a part of the vertical locking system and could be displaced horizontally during locking. The tongue could be for example flexible and resilient in such a way that it can bend along its length and spring back to its initial position.
By “flexible tongue blank” are meant two or more flexible tongues, which are connected to a one-piece component. Examples of such flexible tongue blanks will be described in more detail below.
By “fixing the flexible tongue” is meant that the flexible tongue should at least be sufficiently attached to the floor panel so as not to incidentally fall off during handling of the floor panel, at the factory, during transport and/or in installation. By “mechanically fixed” is meant that the fixing is essentially due to shape or friction force.
By “angling” is meant a connection that occurs by a turning motion, during which an angular change occurs between two parts that are being connected, or disconnected. When angling relates to connection of two floor panels, the angular motion takes place with the upper parts of joint edges at least partly being in contact with each other, during at least part of the motion.
By “vertical folding” is meant a connection of three panels where a first and second panel are in a connected state and where an angling action connects two perpendicular edges of a new panel to the first and second panel. Such a connection takes place for example when a long side of first panel in a first row is already connected to a long side of a second panel in a second row. The third panel is than connected by angling to the long side of the first panel in the first row. This specific type of angling action, which also connects the short side of the new panel and second panel, is referred to as vertical folding
Prior-Art Technique and Problems Thereof
For mechanical joining of long sides as well as short sides in the vertical and horizontal direction (direction D1, D2) several methods are used but the locking is always performed in 3 steps where angling or snapping are combined with displacement along the joint edge in the locked position after an optional side has been joined.                Angling of long side, displacement and snapping-in of short side        Snapping-in of long side, displacement and snapping-in of short side.        Angling of short side, displacement of the new panel along the short side edge of the previous panel and finally downward angling of two panels.        
These laying methods can also be combined with insertion along the joint edge.
It is known that the locking system may, however, be formed so that snapping-in may occur by a motion which is vertical to the surface of the floor panel. Generally, the long side is locked by angling and the short side with a vertical angling which locks with a snap action. Such a system in described in WO 01/0248127 (Akzenta). The connection of panels is complicated and difficult since fibres must be compressed and a hammer with a tapping block must be used. The panels are locked in vertical direction mainly by a friction force and the locking strength is low.
It is known that floor panels may be locked on long and short side vertically and horizontally with one simple vertical folding action (WO 03/083234 Applicant Välinge Aluminium). This document comprises a part of this application. The object of WO 03/083234 is to provide a joint system and floor panels which can be laid with a vertical folding.
A floor panel with a vertical joint in the form of a flexible tongue and a groove is provided, the tongue being made of a separate material and being flexible so that at least one of the sides of the floor panel can be joined by a vertical motion parallel to the vertical plane.
This document also show how a joint system can be made with a flexible spring tongue which can be displaced and/or compressed horizontally in and out or alternatively be bent vertically up or down. It describes a separate tongue of, for instance, wood fibre material, which can be displaced horizontally by means of a flexible material, for instance a rubber paste. It also describes an embodiment with a tongue, which has an inner part that is resilient.
This known technology with a tongue, which during locking moves horizontally in relation to the adjacent edges, offers several advantages over the known installation methods. The locking is easy and faster since 3 steps are reduced to one step.
The invention described in WO 03/083234 does not however show the best mode of locking floor panels with a vertical folding. The production cost and the locking function could be improved considerably.